|Year : 2016 | Volume
| Issue : 3 | Page : 167-171
Micropulse laser for diabetic macular edema
Mahmoud A Abouhussein FRCO Glasgow, MD
Department of Ophthalmology, Faculty of Medicine, Alexandria University, Alexandria, Egypt
|Date of Submission||23-Apr-2016|
|Date of Acceptance||12-Jun-2016|
|Date of Web Publication||6-Dec-2016|
Mahmoud A Abouhussein
9 Hassan Allam Street, Kasr Elmoltazem, Smouha, Alexandria 1103
Source of Support: None, Conflict of Interest: None
The aim of this study was to evaluate the effects of subthreshold micropulse yellow 577-nm laser photocoagulation on eyes with diabetic macular edema (DME).
Patients and methods
In this prospective interventional case series, 20 eyes of 20 patients with previously treated centre involving DME received one single session of yellow micropulse 577-nm laser photocoagulation. Treatment was delivered using the IQ 577-nm laser system. Fixed treatment parameters were used in all cases: 200-µm spot size, 200-ms exposure duration, 400-mW powers, and a 5% duty cycle. Confluent applications with no spacing were administered over the entire edematous area including the fovea.
The baseline best-corrected visual acuity was 0.42±0.15 logMAR, which improved to 0.3±0.26 logMAR at the final follow-up (P<0.043). The central subfield thickness was 354.3±32.96 μm at baseline and the final central subfield thickness was 310.7±52.62 μm (P<0.002).
Subthreshold micropulse yellow 577-nm laser photocoagulation is effective in treating DME.
Keywords: diabetic macular edema, micropulse laser, optical coherence tomography
|How to cite this article:|
Abouhussein MA. Micropulse laser for diabetic macular edema. Delta J Ophthalmol 2016;17:167-71
| Introduction|| |
Diabetic retinopathy (DR) is the most common cause of vision loss in working-aged individuals in developed countries. Diabetic macular edema (DME) is the main cause of decreased vision in DR . It was shown that the 10-year cumulative incidence of DME was 20.1% in patients with type 1 diabetes and 25.4% in patients with type 2 diabetes treated with insulin . The management of DME includes strict glycemic and blood pressure control ,,. Argon laser treatment for clinically significant macular edema has been the mainstay treatment according to the Early Treatment Diabetic Retinopathy Study (ETDRS), which showed a 50% reduction in moderate visual loss following focal laser photocoagulation ,.
The conventional argon laser treatment is associated with application of heat to the surrounding tissues such as the neurosensory retina and the choroid, leading to collateral thermal damage. The grayish endpoint of a laser burn means that the temperature is high enough to alter the transparency of the retina .
Possible side effects of conventional macular laser photocoagulation include visual loss because of accidental foveal photocoagulation, preretinal and subretinal fibrosis, choroidal neovascularization, scotomas, decreased color vision, and progressive expansion of the laser scars into the fovea ,,,.
Conventional laser photocoagulation produces a continuous wave laser output. However, subthreshold micropulse laser treatment delivers laser energy by dividing the beam into a series of short laser pulses. Every single pulse has an on and off duration (duty cycle), enabling tissues to cool down to baseline temperature before the next pulse .
Recent developments in laser science have made it possible to target the retinal pigment epithelium (RPE) with the subthreshold micropulse laser while avoiding harmful effects to the sensory retina and choroid. In 1997, Friberg and Karatza  first reported the clinical application of micropulse 810-nm diode laser treatment in different macular diseases. Evidence suggested that subthreshold laser treatment may be as effective as conventional laser treatment, but with less iatrogenic damage to the tissues surrounding the area of the burn in the RPE ,,,,.
Micropulse subthreshold laser does not exert visible effects on the retina . The beneficial effect of a subthreshold laser might be because of the decreased production of cytokines and vasoactive substances, leading to less capillary permeability . Another theory is that subthreshold laser produces RPE migration and proliferation, leading to drying of the edematous areas . The low level of energy produces no damage to the neurosensory retina, preserving visual function .
Recently, intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) proved to be effective for the treatment of DME, with good visual outcomes . Nevertheless, intravitreal anti-VEGFs are expensive and require repeated injections to maintain the visual and anatomic gain. All intravitreal injections have the potential risk of causing endophthalmitis .
The 577-nm yellow laser wavelength is not absorbed by the xanthophyll pigment in the macula, and is different from the 810-nm infrared laser wavelength in that it is better absorbed by RPE melanin .
The aim of this study was to evaluate the effects of subthreshold micropulse yellow 577-nm laser photocoagulation in eyes with DME.
| Patients and methods|| |
In this prospective interventional case series, 20 eyes of 20 patients, with previously treated centre involving DME, received a single session of yellow micropulse 577-nm laser photocoagulation (Iris Medical OcuLight Slx Laser; Iridex Corp., Mountain View, California, USA).
Inclusion criteria included type 2 diabetes mellitus, HbA1c less than 10, and best-corrected visual acuity (VA) of 0.1 or better on the decimal VA chart. Previously treated eyes with centre involving DME and central subfield foveal thickness between 300 and 400 μm were included.
Exclusion criteria were active proliferative DR, macular ischemia on fluorescein angiography, tractional maculopathy on optical coherence tomography (OCT), vitreous hemorrhage, or media opacity. Patients who received conventional laser, intravitreal injections or had undergone ocular surgery within the previous 6 months were also excluded.
Ethics committee approval was obtained. A written informed consent was provided by the patients after the procedure was explained to them in detail.
At baseline, all patients were subjected to a detailed assessment of history including previous treatment for DME. Complete ophthalmological examination included slit-lamp biomicroscopy with a 90 D lens. VA was determined using a decimal VA chart and the decimal VA was converted into the logarithm of the minimum angle of resolution (logMAR) units for statistical analysis. Fundus photography and fluorescein angiography were performed using a Topcon Fundus Camera (Topcon Corporation, Tokyo, Japan). An OCT examination was performed through a dilated pupil using a commercially available spectral domain Cirrus HD-OCT Model 4000 (Carl Zeiss Meditec Inc., Dublin, California, USA). The scanning protocol used in the study was ‘macular cube 512×128’ scan pattern, where a 6 mm×6 mm area on the retina is scanned with 128 horizontal B-scan lines, each consisting of 512 A-scans per line. The central subfield thickness, which is the central circular zone with a 1-mm diameter, representing the foveal area, was used for the analysis before and after micropulse laser.
Mainster focal grid contact lens (×1.05 laser magnification) was used to perform laser. Fixed treatment parameters were used in all cases: 200-µm spot size, 200-ms exposure duration, 400-mW powers, and a 5% duty cycle. Confluent applications with no spacing were administered over the entire edematous area including the fovea.
Follow-up examinations were performed 1, 3, and 6 months after laser treatment. At each visit, a complete examination was performed with recording of the VA and central subfield thickness on OCT. A comparison was performed between pre-logMAR and post-logMAR VA and OCT central subfoveal thickness at different follow-up visits. Fluorescein angiography was repeated at 6 months.
Data were analyzed using the statistical package for the social sciences (SPSS, version 20; SPSS Inc., Chicago, Illinois, USA) software. The t-test was used for comparisons between different periods of follow-up with the baseline. The level of significance was 0.05.
| Results|| |
The study included 14 women and six men (mean age: 61.3±5.6 years) and the duration of diabetes mellitus in these patients was 12.4±3.76 years. [Table 1] summarizes the baseline characteristics of the patients.
Previous treatment for DME involved the use of a conventional argon laser in six eyes, intravitreal bevacizumab injections in 10 eyes, and both laser and bevacizumab injections in four eyes. On fluorescein angiography, 13 eyes showed focal macular edema and seven eyes showed multifocal macular edema. On OCT, 19 eyes showed cystic changes, 12 eyes showed sponge-like thickening, and two eyes had serous foveal detachment.
The mean number of laser shots was 109.9±47.3 according to the extent of DME.
The baseline best-corrected VA was 0.42±0.15 logMAR, which improved to 0.3±0.26 logMAR at the final follow-up (P<0.043). The central subfield thickness was 354.3±32.96 μm at baseline and the final central subfield thickness was 310.7±52.62 μm (P<0.002). [Table 2] shows a comparison between VA and central subfield thickness at baseline and at different follow-up visits.
|Table 2 Comparison between pretreatment and different follow-up visits of visual acuity and central subfield thickness|
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[Figure 1],[Figure 2],[Figure 3] show a case at baseline, 3 months, and 6 months of follow-up, respectively.
|Figure 1 Before the use of a micropulse laser, the central subfield thickness was 322 μm.|
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|Figure 2 The same patient 3 months after the use of a micropulse laser: the central subfield thickness was 302 μm.|
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|Figure 3 The same patient at the 6-month visit; the central subfield thickness was 285 μm.|
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No complications were recorded from the micropulse laser treatment. No evidence of retinal scars or capillary non perfusion was found on fundus photography or fluorescein angiography at the 6-month follow-up.
In the present study, different OCT patterns did not differ in their response to micropulse laser treatment.
| Discussion|| |
This study evaluated yellow 577-nm micropulse laser in patients with DME. There was an improvement in VA at follow-up visits. The benefit was statistically significant at the 3- and 6-month visits. In terms of the central subfoveal thickness on OCT, there was a decrease in the thickness in all follow-up visits. It was also statistically significant at the 3- and 6-month visits. These results show that the micropulse laser should be used for a long duration to gain beneficial effects. It is not as rapid as intravitreal anti-VEGF injections.
Previous studies have reported the excellent effect of micropulse diode laser treatment on DME in terms of improved VA and decreased thickness on OCT ,,. They reported that micropulse diode laser treatment may have an additional advantage over conventional laser because there is no structural damage in the retinal layers.
Mansouri et al.  studied the effect of initial central foveal thickness on the outcome of subthreshold diode laser treatment in patients with DME. Patients were divided into two groups on the basis of their initial central foveal thickness. Group 1 had central foveal thickness equal to or less than 400 μm; group 2 had central foveal thickness more than 400 μm. They found that group 1 responded better in terms of VA gain and decrease in foveal thickness. They concluded that subthreshold diode macular laser treatment is more effective in patients with mild to moderate DME. Therefore, in the present study, only patients with central subfield thickness less than 400 μm were included.
In their study, Pei-Pei et al.  compared subthreshold with threshold laser grid treatment for patients with DME using a green 532-nm PASCAL system. They found that the mean best-corrected VA and the central macular thickness improved in both the subthreshold group and the threshold group. There was no statistically significant difference between the two groups. They concluded that both 532-nm subthreshold laser grid photocoagulation and threshold laser grid photocoagulation can improve VA and reduce central macular thickness in DME patients.
In another study, Vujosevic et al.  compared the yellow subthreshold micropulse laser with the infrared subthreshold micropulse laser in center involving DME. Central retinal thickness, macular volume, foveal choroidal thickness, and best-corrected VA were not significantly different at any follow-up visit between the two treatment groups. They concluded that both yellow and infrared micropulse laser treatments with the lowest duty cycle (5%) and fixed power parameters seem to be safe and effective in mild center involving DME.
Luttrull and Sinclair  addressed the issue of the ability to treat the fovea directly with a micropulse laser in cases of centre involving DME. They included patients treated with a transfoveal subthreshold diode micropulse laser for fovea involving DME. They reported that no eye showed evidence of laser-induced macular damage by any imaging means postoperatively. There were no adverse treatment effects. The logMAR VA and central foveal thickness improved during follow-up. They concluded that a transfoveal subthreshold diode micropulse laser was safe and effective for the treatment of fovea involving DME in eyes with good preoperative VA. In the present study, the fovea was treated with a 577-nm yellow micropulse laser. No side effects of foveal treatment, using fixed treatment parameters and 5% duty cycle, were detected.
This study has some limitations, notably a relatively small sample size and a short follow-up duration, and absence of macular visual function testing such as contrast sensitivity and microperimetry.
A larger study on a larger number of patients is needed to confirm the benefit of a yellow micropulse 577-nm laser for DME. We need to test the effect in previously untreated eyes in a randomized trial against current treatment options such as intravitreal anti-VEGF drugs or a conventional argon laser.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]